The present invention relates to internal combustion engines. More specifically, the present invention relates to an adjustable cam shaft sprocket for allowing small adjustments to a camshaft.
As is well known, for a four-cycle internal combustion engine to run smoothly, the rotation of the crankshaft and the camshaft must remain in synchronization. Should they fall out of synchronization, serious damage can occur to the engine. Furthermore, it is well known that the maximum horsepower from an engine can be achieved by adjusting the camshaft so that the cams open and close the various engine valves at precisely the right times, thereby improving pumping efficiency.
Generally, in internal combustion engines, a timing chain, belt, or gear is installed around a crank shaft gear, or cam shaft sprocket, mounted on one end of the crank shaft. The timing chain is also installed around a crank shaft gear, which is mounted on one end of a crank shaft. The timing chain thus transfers rotational energy from the crank shaft to the cam shaft sprocket and, hence, the cam shaft. This serves the purpose of not only causing the cam shaft to rotate, but it also maintains the rotational synchronization of these two shafts.
Generally, an engine will operate efficiently within given operating tolerances when the timing chain is installed so that a proper relationship to the drive shaft is achieved. A course adjustment of the cam shaft, and thus, the cams themselves, can be achieved by adjusting the timing chain on the cam shaft gear plus or minus one link in the timing chain. However, this allows only a course adjustment to the cam shaft.
To achieve maximum engine performance, the cam shaft may be further adjusted with respect to the crank shaft by using an adjustable cam shaft sprocket. As shown in FIG. 1a, an adjustable cam shaft sprocket comprises an inner member and an outer member. The inner member is installed concentrically within the outer member, the outer member being toothed for engaging the timing chain. The inner member and the outer member are fastened together using one or more bolts. A fine adjustment of the cam shaft sprocket can be achieved by loosening the bolts, thereby allowing the outer member to be adjusted by any amount with respect to the inner member. When the desired amount of adjustment is achieved, the bolts are tightened so that the inner member and the outer member do not rotate with respect to each other.
One problem with using an adjustable cam shaft sprocket as described above is that over time, the inner member can rotate with respect to the outer member, either by a small amount or a large amount. If the members rotate a small amount with respect to each other, engine performance will suffer. If the members rotate a large amount with respect to each other, a gross misalignment of the cam shaft with respect to the crank shaft will occur, and severe engine damage may result. Rotation between the members occurs because the bolts do not prevent the members from moving with respect to each other. The members are held together by the frictional force between the members that result when the bolts are tightened.
Another method of adjusting a cam shaft is by using a device as shown in FIG. 1b. This device is bolted directly onto the end of a cam shaft and a timing belt or chain is installed around the teeth on the perimeter of the device. The cam shaft has openings which align with one or more holes in the device. When the cam shaft is in the desired position, it is hoped that one of the holes on the device will be aligned with one of the cam shaft openings. If so, then a shear pin is inserted through the aligned openings, and a bolt is tightened to keep the device secured to the end of the cam shaft. If a pair of openings does not align, the belt or chain must be removed and the device repositioned and the hole alignment must be performed again. Even when an initial alignment between openings is achieved, the relative position of the cam shaft with respect to the drive shaft may change slightly due to various factors, such as stretching in the timing belt or chain, and the alignment procedure must be done again. Thus, achieving the desired cam shaft alignment becomes a long, repetitive task.
What is needed is an adjustable cam shaft sprocket that will allow fine adjustments to the cam shaft while preventing rotation between the members with respect to each other during normal engine operation. Ideally, the adjustment would not require removal of the timing belt or timing chain, and would be accomplished in a relatively short period of time.
The present invention is directed to an apparatus for allowing small adjustments to a cam shaft. In one embodiment, the present invention comprises a shear pin and a first circular member having a toothed outer surface for receiving a timing chain or belt, a first cam shaft opening, and a recessed planar surface having a first number of openings located proximate to a perimeter of the recessed planar surface. The present invention further includes a second circular member having a second planar surface and a cylindrical portion extending perpendicularly from the second planar surface, the second planar surface having a cam shaft opening extending through the cylindrical portion and a second number of openings located proximate to a perimeter of the second planar surface, the second circular member for being placed concentrically within said first circular member wherein the second circular member is prevented from rotating with respect to said first circular member by inserting the shear pin through one of the second number of openings and through one of the first number of openings, wherein the second circular member may be adjusted incrementally with respect to the first circular member by removing the shear pin and rotating the second circular member with respect to the first circular member such that a second one of the second number of openings is aligned with a second one of the first number of openings.